This invention relates generally to methods for constructing wells, and, more particularly, to a method for completing a well in a sub-surface geologic formation with unconsolidated sands. Priority is claimed from U.S. Application Ser. No. 09/413,092, filed Oct. 5, 1999, which in turn claims priority from U.S. Provisional patent application Ser. No. 60/103,181, filed on Oct. 5, 1998, incorporated herein by reference.
Methods and apparatus for drilling wells have been in use for many years in a variety of industries, including in the oil production industry. In the oil production industry, wells are constructed downward into sub-surface geologic formations of sand for purposes of withdrawing reservoir fluids (oil, water, gas or the like) or for injecting steam into the formation to heat oil in the formation, which is then more easily withdrawn through an adjacent well. The methods and apparatus vary according to the types of sub-surface geologic formations through which the well passes.
A well typically is formed by incrementally inserting a xe2x80x9cwell casingxe2x80x9d into new sections of well hole. The well casing is a metal pipe through which drilling equipment, reservoir fluids or steam can pass. The well casing extends downward to a sub-surface formation of interest. Well casings that extend downward to end in sub-surface sand formations are subject to xe2x80x9csand inflowxe2x80x9d problems that can partially or wholly obstruct the well. In particular, in situations where a well casing terminates in a sub-surface sand formation, the sand can flow into the well much like sand through an hourglass. Such a sub-surface sand formation is known as an xe2x80x9cunconsolidatedxe2x80x9d sand formation.
Sand inflow is a particular problem where a well casing has more than one hole along its length. A well casing can have multiple holes along its length to allow reservoir fluids to flow into the well from the formation or to allow steam from the well to be injected into the formation. Sand can flow into the well through such holes, obstructing the well casing and possibly obstructing other holes in the well casing as well.
One way to prevent sand inflow is to construct the well with gravel-packed, slotted liners; as is known in the industry. However, such liners are expensive to install and can limit entry of fluid into or out of the well bore. Furthermore, wells with such liners are expensive to repair or modify.
Accordingly, there has existed a need for an improved well completion process that will limit sand inflow from sub-surface geologic formations having unconsolidated sands. The present invention satisfies this need.
The present invention provides a geochemical well completion process that will limit said inflow from formations having unconsolidated sands. In particular, and by way of example only, the well completion process can be used in the construction of wells into sandy formations for the injection of fluid or the removal of reservoir fluids, such as oil, gas, water or the like. The process can also be applied to repairing existing well completions that have been damaged and can no longer prevent sand inflow into the well.
In particular, the invention provides for the application of a geochemical process to complete a new or existing well into a geologic formation consisting of unconsolidated sands utilizing one or more of the below methods, in combination or singly.
One embodiment of the method includes injecting alkaline water into the formation at high temperatures above 250xc2x0 C. and with pH greater than 10 through a limited number of 0.25-0.50 inch diameter perforations to dissolve the sand grains in a near-wellbore region. Significant heat loss and fluid pH reduction occurs in the near-wellbore region as the hot injected fluids go through the perforations, mix with the formation waters, and disperse into the formation sands. The resultant temperature and fluid pH decline rapidly with distance from the wellbore which causes reprecipitation of the dissolved sand grain minerals (primarily calcium, magnesium, aluminum, iron, barium, sodium, sulfur, and silica) into complex synthetic silicate cements which bond the remaining unconsolidated sand grains in the formation around the well to control sand inflow into the well.
Another embodiment applies to geologic formation sands which are unconsolidated but do not contain adequate quantities of the minerals needed to create the complex synthetic silicate cements. The necessary minerals are added and solubilized into the high temperature alkaline water prior to injecting the fluid through the perforations so the dissolved formation sand grains. The supplemental solubilized minerals can react with the formation waters in the near-wellbore region to create the complex synthetic silicate cements to bond the unconsolidated sand grains around the well and thereby control sand inflow into the well.
In another embodiment, the method can include injecting high temperature steam at pressure greater than saturated steam pressures and at steam qualities sufficiently high enough to cause the steam condensate effluent to have an alkaline pH greater than 10. The effluent dissolves the formation sand grains in the near-wellbore region and creates a layer of consolidated sand around the well to thereby control sand inflow into the well.
In yet another embodiment, the method can include injecting high temperature steam at pressures greater than saturated steam pressures and at steam qualities sufficiently high enough to increase the alkalinity of formation waters containing bicarbonates to a pH greater than 10. This dissolves the formation sand grains in the near-wellbore region and create a layer of consolidated sand around the well to control sand inflow into the well. The minerals and fluids that can be used in the aforementioned injection processes are identified in the steam feedwater, formation water, and formation sand analysis contained herein. After completion, the area of sand consolidation is sufficiently rigid to resist sand inflow into the well while remaining porous enough to permit fluid and/or gas flow into or out of the well.
In another embodiment, the method can include locating a sub-surface formation with unconsolidated sands and determining if the one or more of calcium, iron, sulfur, aluminum, barium, magnesium, sodium or silica minerals are in the formation in sufficient quantities for the formation of synthetic cements upon hot water or steam injection. A well is drilled into the formation and a casing is inserted into the well. Perforations are formed in the casing in selected areas of the formation and water is injected water at temperatures of greater than 250xc2x0 C. down the well and through the perforations. The water has a pH greater than 10, thereby consolidating the foundation sand adjacent to the perforation and providing wormholes sufficient for fluid flow between the well and the formation. In another embodiment, one or more of the above minerals is added to the hot water or steam injection if the information is lacking in minerals needed to form synthetic cements.
The novel sand consolidation process can provide substantial well drilling and completion cost savings by eliminating the need for expensive slotted liner or wire wrapped screen liners, by eliminating the need for changeovers to polymer fluid systems. The process can also eliminate under-remaining and gravel pack operations, replacing them with a simple cased-through cemented completion with a reduced number of standard or extreme overbalanced jet perforations. The productivity of the well is not impacted and there is minor or no sand inflow to the well. Since the consolidation procedure allows production and injection wells to be drilled and completed in virtually the same way, the operator can convert the wells back and fourth in an easy fashion.